A Study of Elusive High Density Fluids Surrounding Mineral Inclusions in Gem-quality Kimberlitic Diamonds

Diamonds and their inclusions offer a unique opportunity to learn about the Earth's interior. By studying the chemical compositions and thermodynamic states of inclusions in minerals, geologists and geochemists have been able to make both qualitative and quantitative indirect assessments of the Earth's interior. Diamonds, in particular, are helpful for researching the deep interior of the earth due to their chemically inert nature and strong bond strength, which allows diamonds to preserve, within their inclusions, information about their formation conditions. Fluid inclusions are among the most valuable inclusions found and studied in diamonds. These fluids are known as high density fluids (HDFs) and have been studied mostly in fibrous diamonds. They can provide information on the chemical composition of the formation fluids of the diamonds as well as the circulation of volatiles within the mantle. These HDFs have recently been discovered surrounding solid mineral inclusions in lithospheric gem-quality diamonds from the Udachnaya kimberlitic pipe in the Daldyn-Alakit magmatic region of Russia. The fluids were found to be silicic in composition, and their spatial distribution appeared to be a 1.50µm thick envelope uniformly spread around the inclusions; however, the distribution of the fluids was not the focus of the study. The focus of this study is, therefore, to use Raman Spectroscopy to generate 3D z-stacked images of the inclusions and their fluids around the inclusion in order to gain a better understanding of their distribution. This study will also assess the feasibility of a novel semi-destructive sample preparation method in order to perform a geochemical analysis by using Focused Ion Beam (FIB) milling and Energy Dispersive Spectroscopy (EDS) without breaching the inclusion-fluid cavity, thereby preserving the diamond-inclusion system. The distribution of fluids surrounding the inclusion affects the surface interactions between the host diamond and the inclusion, which may affect their crystallographic orientation relationships (CORs). Due to the scarceness of these fluids and their importance to the study of the earth’s interior developing new non-destructive or semi-destructive methods of analysis are necessary to gain an improved understanding of the fluids and the information they hold. It is possible in this way to check for the presence of ionic compounds in the fluids that would otherwise go undetected due to the limitations of existing analytical methods without compromising the diamond-inclusion system.